The present invention relates to optical devices for the display of luminous or light data collimated to infinity, this data being generally but not obligatorily overlaid on the view of the external landscape. Such devices, with which aircraft are fitted out, may be mounted either on an instrument panel in the head-up position or on a pilot's helmet. They are used mainly as navigational aids and in gun sighting devices.
There is a growing need for light data in aircraft, and the images produced need to have ever bigger fields with an optical quality that should remain sufficient throughout the field, irrespectively of the position of observation of the eyes.
This has gradually led to optical devices having a large number of lenses, at least six of them, hence to optical devices that are bulky and heavy, making it difficult to mount these devices in pilots' helmets.